/*
 * Copyright (C) 2010, 2015 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * membarrier system call
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <linux/syscalls.h>
#include <linux/membarrier.h>

/*
 * Bitmask made from a "or" of all commands within enum membarrier_cmd,
 * except MEMBARRIER_CMD_QUERY.
 */
#define MEMBARRIER_CMD_BITMASK	(MEMBARRIER_CMD_SHARED)

/**
 * sys_membarrier - issue memory barriers on a set of threads
 * @cmd:   Takes command values defined in enum membarrier_cmd.
 * @flags: Currently needs to be 0. For future extensions.
 *
 * If this system call is not implemented, -ENOSYS is returned. If the
 * command specified does not exist, or if the command argument is invalid,
 * this system call returns -EINVAL. For a given command, with flags argument
 * set to 0, this system call is guaranteed to always return the same value
 * until reboot.
 *
 * All memory accesses performed in program order from each targeted thread
 * is guaranteed to be ordered with respect to sys_membarrier(). If we use
 * the semantic "barrier()" to represent a compiler barrier forcing memory
 * accesses to be performed in program order across the barrier, and
 * smp_mb() to represent explicit memory barriers forcing full memory
 * ordering across the barrier, we have the following ordering table for
 * each pair of barrier(), sys_membarrier() and smp_mb():
 *
 * The pair ordering is detailed as (O: ordered, X: not ordered):
 *
 *                        barrier()   smp_mb() sys_membarrier()
 *        barrier()          X           X            O
 *        smp_mb()           X           O            O
 *        sys_membarrier()   O           O            O
 */
SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
{
	if (unlikely(flags))
		return -EINVAL;
	switch (cmd) {
	case MEMBARRIER_CMD_QUERY:
		return MEMBARRIER_CMD_BITMASK;
	case MEMBARRIER_CMD_SHARED:
		if (num_online_cpus() > 1)
			synchronize_sched();
		return 0;
	default:
		return -EINVAL;
	}
}
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<div class='path'>path: <a href='/cgit.cgi/linux/net-next.git/commit/?id=a57cb1c1d7974c62a5c80f7869e35b492ace12cd'>root</a>/<a href='/cgit.cgi/linux/net-next.git/commit/Documentation?id=a57cb1c1d7974c62a5c80f7869e35b492ace12cd'>Documentation</a></div><div class='content'><div class='cgit-panel'><b>diff options</b><form method='get'><input type='hidden' name='id' value='a57cb1c1d7974c62a5c80f7869e35b492ace12cd'/><table><tr><td colspan='2'/></tr><tr><td class='label'>context:</td><td class='ctrl'><select name='context' onchange='this.form.submit();'><option value='1'>1</option><option value='2'>2</option><option value='3' selected='selected'>3</option><option value='4'>4</option><option value='5'>5</option><option value='6'>6</option><option value='7'>7</option><option value='8'>8</option><option value='9'>9</option><option value='10'>10</option><option value='15'>15</option><option value='20'>20</option><option value='25'>25</option><option value='30'>30</option><option value='35'>35</option><option value='40'>40</option></select></td></tr><tr><td class='label'>space:</td><td class='ctrl'><select name='ignorews' onchange='this.form.submit();'><option value='0' selected='selected'>include</option><option value='1'>ignore</option></select></td></tr><tr><td class='label'>mode:</td><td class='ctrl'><select name='dt' onchange='this.form.submit();'><option value='0' selected='selected'>unified</option><option value='1'>ssdiff</option><option value='2'>stat only</option></select></td></tr><tr><td/><td class='ctrl'><noscript><input type='submit' value='reload'/></noscript></td></tr></table></form></div><table summary='commit info' class='commit-info'>
<tr><th>author</th><td>Linus Torvalds &lt;torvalds@linux-foundation.org&gt;</td><td class='right'>2016-12-14 17:25:18 -0800</td></tr>
<tr><th>committer</th><td>Linus Torvalds &lt;torvalds@linux-foundation.org&gt;</td><td class='right'>2016-12-14 17:25:18 -0800</td></tr>
<tr><th>commit</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/Documentation?id=a57cb1c1d7974c62a5c80f7869e35b492ace12cd'>a57cb1c1d7974c62a5c80f7869e35b492ace12cd</a> (<a href='/cgit.cgi/linux/net-next.git/patch/Documentation?id=a57cb1c1d7974c62a5c80f7869e35b492ace12cd'>patch</a>)</td></tr>
<tr><th>tree</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/tree/?id=a57cb1c1d7974c62a5c80f7869e35b492ace12cd'>5a42ee9a668f171143464bc86013954c1bbe94ad</a> /<a href='/cgit.cgi/linux/net-next.git/tree/Documentation?id=a57cb1c1d7974c62a5c80f7869e35b492ace12cd'>Documentation</a></td></tr>
<tr><th>parent</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/Documentation?id=cf1b3341afab9d3ad02a76b3a619ea027dcf4e28'>cf1b3341afab9d3ad02a76b3a619ea027dcf4e28</a> (<a href='/cgit.cgi/linux/net-next.git/diff/Documentation?id=a57cb1c1d7974c62a5c80f7869e35b492ace12cd&amp;id2=cf1b3341afab9d3ad02a76b3a619ea027dcf4e28'>diff</a>)</td></tr><tr><th>parent</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/Documentation?id=e1e14ab8411df344a17687821f8f78f0a1e73cbb'>e1e14ab8411df344a17687821f8f78f0a1e73cbb</a> (<a href='/cgit.cgi/linux/net-next.git/diff/Documentation?id=a57cb1c1d7974c62a5c80f7869e35b492ace12cd&amp;id2=e1e14ab8411df344a17687821f8f78f0a1e73cbb'>diff</a>)</td></tr></table>
<div class='commit-subject'>Merge branch 'akpm' (patches from Andrew)</div><div class='commit-msg'>Merge more updates from Andrew Morton:

 - a few misc things

 - kexec updates

 - DMA-mapping updates to better support networking DMA operations

 - IPC updates

 - various MM changes to improve DAX fault handling

 - lots of radix-tree changes, mainly to the test suite. All leading up
   to reimplementing the IDA/IDR code to be a wrapper layer over the
   radix-tree. However the final trigger-pulling patch is held off for
   4.11.

* emailed patches from Andrew Morton &lt;akpm@linux-foundation.org&gt;: (114 commits)
  radix tree test suite: delete unused rcupdate.c
  radix tree test suite: add new tag check
  radix-tree: ensure counts are initialised
  radix tree test suite: cache recently freed objects
  radix tree test suite: add some more functionality
  idr: reduce the number of bits per level from 8 to 6
  rxrpc: abstract away knowledge of IDR internals
  tpm: use idr_find(), not idr_find_slowpath()
  idr: add ida_is_empty
  radix tree test suite: check multiorder iteration
  radix-tree: fix replacement for multiorder entries
  radix-tree: add radix_tree_split_preload()
  radix-tree: add radix_tree_split
  radix-tree: add radix_tree_join
  radix-tree: delete radix_tree_range_tag_if_tagged()
  radix-tree: delete radix_tree_locate_item()
  radix-tree: improve multiorder iterators
  btrfs: fix race in btrfs_free_dummy_fs_info()
  radix-tree: improve dump output
  radix-tree: make radix_tree_find_next_bit more useful
  ...
</div><div class='diffstat-header'><a href='/cgit.cgi/linux/net-next.git/diff/?id=a57cb1c1d7974c62a5c80f7869e35b492ace12cd'>Diffstat</a> (limited to 'Documentation')</div><table summary='diffstat' class='diffstat'>